De-pilers, or unpiling apparatus, have been used for quite some time. The normal application is in conjunction with a power station or other coal burning facility wherein large piles of coal are dumped over openings in the ground which lead into tunnels communicating with the furnace or other place of ultimate use. In such installations, a cylindrical hopper is located in the opening beneath the pile and the hopper can be vibrated in order to deliver material from the pile into a feeder. The feeder feeds the material delivered thereto at a regulated rate, the outlet of the feeder being connected to a conveyor such as a belt or the like which carries the coal at a predetermined rate to a furnace or other place of use. While feeders in the system just described normally operate constantly, the hoppers are operated at spaced intervals with periods of rest therebetween. This is normally because the delivery rate of the hoppers far exceeds the requirement of the feeders, and if the hoppers were vibrated with material therein which was not being discharged, the material would tend to pack and eventually bridge, causing cessation of flow.